Azeotropic composition containing hexafluoroacetone,hydrogen fluoride,and trichlorotrifluoroethane



United States Patent U.S. Cl. 25260 Int. Cl. C09k 3/00 1 Claim ABSTRACTOF THE DISCLOSURE CF COCF HF and CCl FCClF form a constant boilingazeotrope which, at about atmospheric pressure, boils at about 13 C. andcontains about 44 mole percent of CF COCF about 42.2 mole percent HF andabout 13.8 mole percent of CCl FCClF This is a division of applicationSer. No. 487,917 filed Sept. 16, 1965, and now Patent No. 3,406,099.

This invention relates to a novel azeotropic composition and its use inazeotropic distillation procedures. More particularly, the inventionrelates to a novel azeotropic mixture of CF COCF (hexafluoroacetone), HF(hydrogen fiuoride) and CCl FCClF (l,l,2-trichlorotrifiuoroethane) andto a procedure for separating CF COCF HF or CCl FCClF from mixturescontaining one or more of these materials. In a preferred embodiment theinvention relates to separating CCl FCClF from mixtures containing itand dichlorotetrafluoroacetone (symor unsym-).

In the production of dichlorotetrafluoroacetone from hexachloroacetone,or other lesser fluorinated perchlorofluoroacetones, with HP in liquidphase, in the presence of an antimony catalyst (the subject of US.Patent 2,853,524 to Miller and Woolf), CCl FCClF is unavoidably formedas a decomposition product. For commercial development applications, itis desirable to obtain dichlorotetrafluoroacetone at least about 99%pure. Since both symand unsym-dichlorotetrafluoroacetone (hereinaftergenerically referred to as 4FK) have boiling points of about 45 C. andCCl FCClF has a boiling point of about 47 C., separation of CCl FCClFfrom 4FK by distillation is extremely difiicult and purification, inlarge amounts, by ordinary distillation to substantially more than 99%is not at all feasible.

We have found, quite unexpectedly, that CF COCF (B.P. -27.7 C.), HF(B.P. 19.5 C.) and CCI FCCIF (B.P. 47.7 C.) when mixed together, form aconstant boiling azeotrope boiling at about 13 C. at about atmosphericpressure and having a weight percent composition of 68.0:7.9:24.1 or amolar percent composition of 44.0:42.2:13.8, or about a 414:1 molarratio of We have also found that this azeotrope can be used to separateCF COCF HF or CCI FCCIF from mixtures containing one or more of thesematerials, provided that other components of the mixture do not possessboiling points unduly close to the boiling point of the azeotropicmixture (i.e., about 13 C.) and provided that other components in themixture do not interfere with the formation of the azeotrope.

We have further found that this method is particularly effective forseparating CCl FCClF from 4FK..

It is accordingly an object of this invention to provide a novelconstant boiling azeotropic mixture containing the components CF COCF HFand CCIzFCClFg.

It is another object of the invention to provide an azeotropicdistillation procedure for separating CF COCF HF or CCI FCCIF frommixtures containing one or more of these materials.

A particular object of the invention is to provide an azeotropicdistillation procedure for purifying 4FK.

Other objects and advantages of the invention will be come apparent fromthe following description.

The azeotrope of the invention is easily formed by bringing together itscomponents in proper proportions, or by bringing together the componentsin any proportions followed by distillation to remove excess CF COCF(B.P. 27.7 C.) as distillate and recovery of the azeotrope as distillateleaving a residue of HF and CCl FCClF In use of the azeotrope inazeotropic distillation procedures, there need only be added sufficientamount(s) of the lacking component(s) to completely tie up the remainingcomponent(s). For instance, in the preferred embodiment, crudefi-uoroketone product from a liquid phase antimony pentahalide catalyzedfluorination procedure, as described heretofore, is supplied with enoughand HF in order to quantitatively tie up the undesired CCl FCClF as theinvention azeotrope. Precise quantitative amounts need not be employedas long as there is enough CF COCF and HF present to completely tie upthe CCl FCClF Large excesses of CF COCF (B.P. 27.7 C.) and HF (B.P. 19.5C.) will not deleteriously affect the purification procedure for 4FK(B.P. 45 C.) since the boiling points of these materials aresutficiently distinct as to permit effective separation by ordinarydistillation means.

Operating pressures during the azeotropic distillation procedures arenot critical and may be atmospheric, subatmospheric or superatmospheric.Atmospheric pressure is usually most convenient and is thereforepreferred.

Apparatus suitable for preparation of the azeotrope includes vertuallyany vessel or system in which contact of the three components can beeffected, the materials of which are inert to the components. Glass, forinstance, should be avoided because of the use of HF. Normally, theazeotrope is formed in the purification apparatus in situ. Suchapparatus may be of conventional design for azeotropic distillations andtypically includes a fractionating column provided with a reboiler atthe bottom and a condenser connected to the top, which condenser is inturn provided with suitable cooling means. Conventional continuousdistillation apparatus may be employed, as well as batch-type stills.

The same principles and techniques may be used to separate any of CFCOCF HF or CCl FCClF from mixtures containing the same with thelimitations mentioned heretofore. Other applications will readily occurto those of ordinary skill in the art and potential interference ofother materials in the mixture with formation of the azeotrope can beascertained by routine testing.

The following illustrate practice of the invention:

EXAMPLE 1 A Monel still provided with a 5' x 1%." column, a reboiler ofabout one gallon capacity and a condenser equipped with a cold methanolcirculation pump was evacuated and, at room temperature, was chargedwith an equimolar mixture of CCI FCCIF (750 g.) and HF g.). An equimolaramount (637 g.) of CF COCF Was then bubbled into the liquid in the stillthrough a dip line. While the CF COCF was charged, the overheadcondenser was maintained at about 60 C. About half of the still contentswere distilled off at about 15 p.s.i.a. A large fraction was recoveredat about 13 C. Gas chromatographic analysis showed that this fractionconsisted of about 7.9 weight percent (42.2 mole percent) 3 HF, 68.0weight percent (44.0 mole percent) CF COCF and 24.1 weight percent (13.8mole percent) CCl FCClF EXAMPLE 2 A crude charge, from a liquid phaseantimony pentahalide catalyzed HF fluorination of hexachloroacetone,obtained substantially as described in U.S. Patent 2,853,524, containing191 lbs. of 4FK and 5 lbs. of CC1 FCClF was subjected to a batchdistillation procedure in a 4" ga. steel still, similar to thatdescribed in Example 1. 158 lbs. of 4FK, containing an average of 2.6%by weight of CCl FCClF was obtained, as ascertained by gaschromatographic analysis. Of this amount only 21 lbs. of 4FK wereobtained that contained less than 1% by weight of CCl FCClF A secondbatch distillation was carried out in the same apparatus, with a crudecharge from the same source, as described above, which contained 141lbs. of 4FK and 3 lbs. of CCl FCClF In the second distillation, however,17 lbs. of HF and 6 lbs. of CF COCF quantities considerably more thanenough to form the azeotrope, were added to the charge prior todistillation. In the ensuing distillation, 140 lbs. of 4FK containingless than 0.155 by weight of CCl FCClF were recovered.

We claim:

1. An azeotropic composition, which at about atmospheric pressure,contains about 44 mole percent of CF COCF about 42.2 mole percent of HFand about 13.8 mole percent of CCl FCClF and boils at about 13 C.

References Cited UNITED STATES PATENTS 9/1961 Eiseman 252-67 7/1968Eiseman s 252-67 OTHER REFERENCES Azeotropic Data, American ChemicalSociety, 1952, p. 5.

International Encyclopedia of Chemical Science, Van Nostrand Co., 1964,p. 96.

LEON D. ROSDOL, Primary Examiner I. GLUCK, Assistant Examiner U.S. Cl.X.R.

553 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,490,739 Dated January 20, 1970 Inventofls) Walter R. Buckman and.William R. Clemons It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 7, after the zip code "7071 the following words should beinserted: -,Ass1gnors to Allied Chemical Corporation, New York, NewYork, a corporation of New York-- Sibi'iiil MN mum (SEAL) AMEdumllbl'lamhml mm I. m a

AW Officer Dominicanol mm

